THE NUTRITIONAL ECOLOGY OF A PARASITOID WASP, EPHEDRUS-CALIFORNICUS BAKER (HYMENOPTERA, APHIDIIDAE)

We tested the hypothesis that the pattern of development and growth of a generalist parasitoid wasp varies in different hosts. We reared Eph edrus californicus Baker (Hymenoptera: Aphidiidae), a solitary parasit oid of aphids, under controlled laboratory conditions on five kinds of hosts: nymphal instar 1 (24 h old), 2 (42 h), 3 (96 h), and 4 (144 h) of apterous virginoparae of Acyrthosiphon pisum (Harris), and nymphal instar 1 (24 h) of Macrosiphum creelii Davis (Homoptera: Aphididae). Parasitoid dry mass increased with the host instar at parasitization. Females were larger than males although the degree of sexual size dimo rphism declined with increased host size. Development time from ovipos ition to adult eclosion varied non-linearly with the host instar at pa rasitization, and was shortest in first and fourth nymphal instars. Pa rasitoids developing in M. creelii gained more mass in less time than their counterparts developing in A. pisum of the same initial size. In low-quality hosts, parasitoids apparently trade off increased develop ment time for a gain in adult mass. A possible explanation of sexual s ize dimorphism in E. californicus is that large females may be able to overcome aphid defensive behaviours better than small ones.